For a utility operating a nuclear reactor system, it is imperative that Inservice Inspection (ISI) of the reactor system welds be performed as rapidly as possible without sacrificing accuracy. The inspection system is comprised of mechanical positioning equipment and nondestructive examination instrumentation. It is desirable to reduce the time in making these inspections without reducing the quality of the examinations. Reduction in this time will enable the utility to realize savings in operating costs due to shorter downtimes and a reduction in radiation exposure to examination personnel.
The present rules for ISI, established by the ASME Code, Section XI "Rule for Inservice Inspection of Nuclear Power Plant Components", require a complete inspection of reactor vessel welds every ten operational years. In addition, it is a USNRC requirement that personnel radiation exposure be "as low as reasonably achievable." Hence, it is inevitable, based on these criteria and the very high cost of plant downtime, that an inspection agency must provide reliable, accurate, and rapid inspection techniques.
The inservice inspection program includes both the component and piping welds. In general, there are numerous access problems, weld configuration variations and radiation hazards that must be considered. The inservice inspection tool is mounted on the flange of the nuclear vessel and manipulated beneath many feet of radiation-shielding water. The area to be inspected in and about the nuclear vessel is reached with predetermined location information, supplemented by TV cameras. The ISI tool, from its mount on the reactor vessel flange, is capable of reaching all areas of the reactor vessel by actuating rotating and telescoping booms along with specially designed fixtures that hold the ultrasonic search units.
The operating console for this tool contains the necessary controls and instruments for manifesting readout information for both the inspection booms and attachments. The controller allows the operator to move the search units accurately through all the required examination regions and provides precise position data. By enhancing the versatility of the inspection equipment, the number and frequency of mechanical configuration changes can be reduced. This has resulted in a reduction in setup time and, equally important, greatly reduced handling of contaminated parts. This versatility is achieved by means of remote or preprogramed articulation of ultrasonic weld entry angles. The prior art approach to this problem is to use several transducers preset at specific sound angles. This method has the disadvantage of increased size and weight, resulting in an inability to inspect close to obstructions and requiring massive manipulating equipment and changes of sleds on which the transducers are mounted.
Means are needed to remotely and automatically change the transducer angles, enabling the inspection of weld volumes adjacent to obstructions and in areas of complex geometry. This technique will particularly improve the inspection of the reactor vessel nozzle-to-shell weld where the weld configuration has a complex geometry represented by the inspection of two cylinders. In order to perform this examination with the sound angle parallel to the weld centerline, the sound angle must be skewed continuously through a predetermined angle with respect to the vessel surface as the search unit is translated along the weld.